Controlled mini-emulsion free radical polymerisation

ABSTRACT

The invention concerns a method for preparing polymers by free radical polymerisation comprising (i) preparing a mini-emulsion containing: at least an ethylenically unsaturated monomer, at least a control agent selected among xanthates, dithio-carbamates, thioether-thiones, the xanthates comprising phosphorus and optionally fluorine and dithiophosphoroesters, an aqueous solution, a surfactant, and a co-surfacant, and (ii) reacting said mini-emulsion, in the presence of a free radical source, at a sufficient temperature and/or for a sufficient time interval to form the polymers.

[0001] The present invention relates to a novel process for miniemulsionradical polymerization providing access to polymers possessingreactivateable chain ends which can be used in particular for thepreparation of block copolymers.

[0002] Emulsion polymerization is currently the most advancedpolymerization process industrially. Mention may be made, among the mostwell-known products, of styrene-butadiene copolymers, vinyl acetate andacrylic latexes.

[0003] A standard emulsion free radical polymerization process involvesthe following compounds: water, a monomer or a mixture of monomers, atleast one surfactant, an initiator and optionally polymerizationadditives (transfer agents, salts). In outline, the monomers aredistributed in the following way:

[0004] very predominantly in the form of droplets dispersed in theaqueous phase and stabilized by the surfactant,

[0005] at the core of surfactant micelles,

[0006] soluble, at a low concentration, in the aqueous phase.

[0007] The reaction begins by the creation of radicals in the aqueousphase resulting from the decomposition of the water-soluble initiator.These radicals initiate chains which propagate in the aqueous phaseuntil a critical size is reached, at which these chains precipitate andnucleate a particle. The very low specific surface of the droplets,combined with their number, renders their nucleation improbable incomparison with that of the micelles. Nucleation takes place verypredominantly in ,swollen micelles of the monomers, which are nucleatedto give particles of polymers. The supplying of the particles withmonomers is therefore provided by the droplets, which act as a reservoirof monomers which diffuses toward the polymerization sites.

[0008] Ugelstad has demonstrated (Ugelstad et al., Journal of PolymerScience, Polym. Letter Ed., 111, 503 (1973)) that, when the droplets ofmonomers are prepared by a miniemulsification process to producedroplets of submicron size, the nucleation of the droplets may no longerbe neglected. Below a certain size of droplets, this mechanism becomespredominant, to become the only mechanism if the splitting of thedroplets becomes sufficiently great. Ideally, in the absence of anysubsidiary nucleation, this means that the number and the size of theparticles are identical to those of the starting droplets. This scenariocan introduce a number of advantages. First of all, the distributions insize of particles are generally broad, which makes it possible toenvisage the preparation of latexes possessing very high levels ofsolids (greater levels than the conventional emulsion process—Masa etal., J. Appl. Polym. Sci., 48, 205 (1993)). It has also beendemonstrated that the miniemulsion has a distinct advantage incontrolling the size of the particles during polymerization processes inCSTR (Continuous Stirred Tank Reactors) reactors (Aizpurua et al.,Macromol. Symp., 111, 121 (1996)).

[0009] Specific radical polymerization processes have recently beendeveloped in which the polymer chains produced are functionalized by endgroups capable of being able to be reactivated in the form of freeradicals by virtue of reversible transfer or termination reactions.

[0010] This type of specific radical polymerization is generally denotedby the term of “controlled” or “living” radical polymerization. Thesenames originate from the fact that the presence of the reactivateableend groups described above brings about the existence of equilibriabetween functionalized entities (known as “dormant” entities) and activeentities (free radicals), which makes it possible both to control thegrowth of the polymer chains (acquisition of narrow distributions in themasses and control of the average molecular mass, in particular byvarying the monomer/precursor of active chains molar ratio) and toobtain functionalized polymers, known as “living” polymers, capable ofbeing employed as reactivateable entities in subsequent radicalpolymerization reactions, which proves to be particularly advantageousin the context of the preparation of block copolymers.

[0011] The controlled radical polymerization can make it possible toexhibit the following distinct aspects:

[0012] 1. the number of chains is unchanging throughout the duration ofthe reaction,

[0013] 2. the chains all grow at the same rate, which is reflected by:

[0014] a linear increase in the molecular masses with the conversion,

[0015] a narrow distribution in the masses,

[0016] 3. the average molecular mass is controlled by the monomer/chainprecursor molar ratio,

[0017] 4. the possibility of preparing block copolymers.

[0018] The controlled nature becomes more pronounced as the rate ofreactivation of the chains to radicals becomes greater in comparisonwith the rate of growth of the chains (propagation). Cases exist wherethis is not always true (i.e. the rate of reactivation of the chains toradicals is less than the rate of propagation) and conditions 1 and 2are not observed. Nevertheless, it is still possible to prepare blockcopolymers.

[0019] Recently, processes for living radical polymerization byreversible addition-fragmentation transfer have been developed. Thisspecific type of polymerization constitutes one of the most appropriatetechnologies for synthesizing block copolymers by the radical route. Inthis context, patent applications WO 98/01478, on behalf of Dupont deNemours, and WO 99/35178, on behalf of Rhodia Chimie, disclose, forexample, the use of control agents of dithioester type of RS(C═S)R′ typefor the synthesis of controlled-architecture copolymers. The control ofradical polymerizations by dithiocarbamates of type RS(C═S)NR′R″ hasalso recently been disclosed in patent applications WO 99/35177 onbehalf of Rhodia Chimie and WO 99/31144 on behalf of Dupont de Nemours.In the context of the living radical polymerization, xanthates ofgeneral formula RSC(═S)OR′, disclosed, for example, in patentapplication WO 98/58974 on behalf of Rhodia Chimie, are particularlyadvantageous reversible transfer agents which make it possible tocontrol the radical polymerization of a large number of monomers, suchas styrene, acrylic, acrylamide, vinyl ester and diene monomers.

[0020] In a conventional emulsion, the agents for control via areversible termination reaction, such as the nitroxide precursorsaccording to the teaching of patent application WO 99/03894 or theorganometallic complex in the oxidized state in ATRP (Atom TransferRadical Polymerization) technology according to the teaching ofapplication WO 96/30421, can be distributed between the organic phaseand the aqueous medium. If an excessively high proportion of deactivatoris present in the aqueous phase, reversible termination reactions takeplace at this spot. The main consequence is a decrease in thepolymerization rate. A lack of control agent in the effectivepolymerization site, namely the particles, brings about a loss incontrol of the reaction. The main result of this is a broadening in themolecular mass distribution. Furthermore, from a kinetic view point, thenitroxide and ATRP technologies are unfavorable in a dispersed mediumapproach. Very slow polymerizations result therefrom.

[0021] The nitroxide technology was employed in a conventional emulsion(Lansalot et al., ACS Polymer Preprints, Division of Polymer Chemistry,40 (2), 317 (1999)) and in a miniemulsion (Xerox Corporation patent U.S.Pat. No. 6,121,397). The major disadvantage of this family of agents istheir application in a dispersed medium to a very limited number ofmonomers, mainly styrene and dienes.

[0022] In the case of ATRP, the distribution of the catalyst between theaqueous phase and the organic phase is mainly determined by the natureof the ligand. It has been demonstrated that the ligand has to besufficiently hydrophobic to introduce a minimum of catalyst into theorganic phase. However, conversely, if the complex becomes toohydrophobic, the diffusion of the catalyst through the aqueous phasebecomes too slow, which has the effect of detrimentally affecting thequality of the control of the polymerization. To keep the copper-basedcatalyst in the particles, Matyjaszewski et al., (Journal of PolymerScience, vol. 38, 4724 (2000)) have had a miniemulsion approach. A majordisadvantage of this system is the fact of being able to use solelynonionic surfactants, moreover in a very large amount (more than 10%with respect to the monomers in the conventional procedures).

[0023] Systems based on reversible transfer are more favorable, on theone hand kinetically but in particular because of the creation ofcontrol macroagents (chains of polymers), once the first transferreaction has been carried out between the initial control agent and aradical growing in the organic phase. This situation prevents anydeparture of the control agent thus created from the particle.

[0024] However, several disadvantages of these techniques could bedetected in a conventional emulsion. This is the case when the controlagent diffuses more slowly into the aqueous phase than the monomer. Thisgenerally results in poorly controlled number-average molecular massesMn and high polydispersity indices. Mention may thus be made inparticular of Lansalot et al., Macromolecules, 32, 7354 (1999), for theuse of C₆F₁₃I as reversible transfer agent in the emulsionpolymerization of styrene. A miniemulsion use has been introduced inorder to circumvent this difficulty.

[0025] Another well-known system is thus reversibleaddition-fragmentation transfer. One of the families of control agentscoming within this category is that of the dithioesters RS(C═S)R′, asindicated above. Because of their very high transfer constant,dithioesters RS(C═S)R′ possessing a tertiary R leaving group areentirely ineffective as reversible addition-fragmentation agents inconventional emulsion polymerization (Hans de Brouwer et al.,Macromolecules, 2000, 33, 9239). They are only active in a miniemulsionin the presence of exclusively nonionic surfactant, in an amount ofgreater than 10% generally, which greatly restricts the potential of useof such systems. Examples of living polymerization synthesis in aminiemulsion have been given in patent application WO 98/01478 in thepresence of benzyl dithiobenzoate as control agent; however, only thesynthesis of polystyrene, thus of homopolymers, is described therein.

[0026] One aim of the present invention is thus to provide a novelprocess employed in a miniemulsion which makes it possible to obtainhigh yields of polymers.

[0027] A second aim of the invention is to provide a process for thesynthesis by radical polymerization of block polymers, in particular oftriblock polymers, with a lower polydispersity index than for a standardemulsion process employing the same reactants.

[0028] A third aim is to provide a radical polymerization process whichis easy and inexpensive to implement.

[0029] These aims and others which will become apparent in thecontinuation of the description are achieved by the present invention,which relates to a process for the preparation of polymers by radicalpolymerization which comprises (i) the preparation of a miniemulsioncomprising:

[0030] at least one ethylenically unsaturated monomer,

[0031] at least one control agent selected from xanthates,dithiocarbamates, thioether-thiones, xanthates comprising phosphorus andoptionally fluorine and dithiophosphoric acid esters,

[0032] an aqueous solution,

[0033] a surfactant,

[0034] and a cosurfactant,

[0035] and (ii) the reaction of said miniemulsion, in the presence of asource of free radicals, at a sufficient temperature and/or for asufficient time to form polymers.

[0036] The process according to the invention exhibits the advantage ofbeing able to easily and efficiently prepare triblock polymers in adispersed medium.

[0037] It also exhibits the advantage of making it possible to obtainrelatively high solid contents (from 10 to 65%, preferably from 30% to50%, by weight).

[0038] In the present description, and in the absence of contraryindications, the term “polymer” will be used to denote, within the broadsense, both homopolymers and copolymers.

[0039] Furthermore, within the meaning of the invention, the term “blockcopolymer” is understood to mean a copolymer comprising at least twosuccessive sequences (blocks) of monomer units with different chemicalconstitutions. Each of the blocks present can be composed of ahomopolymer or of a copolymer obtained from a mixture of ethylenicallyunsaturated monomers. In the second case, the block can in particular bea random copolymer. The block copolymers within the meaning of theinvention can thus comprise two blocks each composed of randomcopolymers. In this case, the ethylenically unsaturated monomers aresuch that the blocks obtained are of different natures. The term “blocksof different natures” is understood to mean either blocks composed ofmonomers of different types or blocks composed of monomers of the sametype but in different amounts.

[0040] Mention may in particular be made, among control agents which canthus be used to prepare the polymer or polymers, of reversibleaddition-fragmentation agents of xanthates type RSC═SOR′, such asdescribed in patent applications WO 98/58974 and WO 00/75207,dithiocarbamates of formula RS(C═S)NR₁R₂, such as those described inpatent applications WO 99/35177 and WO 99/31144, or thioether-thionecompounds, such as those described in patent application FR 2 794 464.

[0041] Mention may also be made of compounds of the family of thexanthates comprising phosphorus and optionally fluorine, such as thosedescribed in French patent application No. 2 802 208, filed by theApplicant Company.

[0042] Mention may additionally be made of dithiophosphoric acid estercompounds, such as those of general formula (B) which were described inFrench patent application No. 00/09952, filed by the Applicant Company:

[0043] in which:

[0044] R₁ represents:

[0045] an optionally substituted alkyl, acyl, aryl, aralkyl, alkene oralkyne group,

[0046] an optionally substituted, saturated, unsaturated or aromatic,carbonaceous ring or heterocycle,

[0047] a polymer chain,

[0048] R₂ and R₃, which are identical or different, represent:

[0049] a hydrogen atom,

[0050] —S—R₁,

[0051] an optionally substituted alkyl, acyl, aryl, aralkyl or alkyneradical,

[0052] an optionally substituted, saturated, unsaturated or aromatic,carbonaceous ring or heterocycle,

[0053] R₂ and R₃ can together represent the atoms necessary to form anoptionally substituted, saturated, unsaturated or aromatic, carbonaceousring or heterocycle, and

[0054] p is between 2 and 10.

[0055] The R₁, R₂ and R₃ groups, when they are substituted, can besubstituted by substituted phenyl groups, substituted aromatic groups,saturated or unsaturated carbonaceous rings, saturated or unsaturatedheterocycles, or groups: alkoxycarbonyl or aryloxycarbonyl (—COOR),carboxyl (—COOH), acyloxy (—O₂CR), carbamoyl (—CONR₂), cyano (—CN),alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkycarbonyl,phthalimido, maleimido, succinimido, amidino, guanidino, hydroxyl (—OH),amino (—NR₂), halogen, perfluoroalkyl C_(n)F_(2n+1), allyl, epoxy,alkoxy (—OR), S-alkyl, S-aryl, groups exhibiting a hydrophilic or ionicnature, such as alkaline salts of carboxylic acids, alkaline salts ofsulfonic acid, poly(alkylene oxide) (PEO, PPO) chains, cationicsubstituents (quaternary ammonium salts), R representing an alkyl oraryl group, or a polymer chain.

[0056] According to a specific embodiment, R1 is a substituted orunsubstituted, preferably substituted, alkyl group.

[0057] The compounds of formula (B) of use as control agents forpreparing first generation polymers are, for example, the compounds inwhich R₁ is selected from:

[0058] —CH₂C₆H₅

[0059] —CH(CH₃)(CO₂Et)

[0060] —CH(CH₃)(C₆H₅)

[0061] —CH(CO₂Et)₂

[0062] —C(CH₃)(CO₂Et) (S—C₆H₅)

[0063] —C(CH₃)₂(C₆H₅)

[0064] —C(CH₃)₂CN

[0065] in which Et represents an ethyl group and Ph represents a phenylgroup.

[0066] The compounds of formula (B) are readily accessible. They can inparticular be obtained by reaction between P₄S₁₀, K₂CO₃ and ahalogenated derivative (Nizamov et al., Phosphorus, Sulfur and Silicon,vol. 132, 85-100 (1998)). Another access route consists in reacting analkali metal salt of a dithiophosphonic acid with a halogenatedderivative (Mastryukova et al., Bull. Acad. Sci. USSR. Div. Chem. Sci.(Engl Transl), vol. 27, 1917 (1978)).

[0067] The optionally substituted alkyl, acyl, aryl, aralkyl or alkynegroups generally exhibit 1 to 20 carbon atoms, preferably 1 to 12 andmore preferably 1 to 9 carbon atoms. They can be linear or branched.They can also be substituted by oxygen atoms, in the form in particularof esters, or sulfur or nitrogen atoms.

[0068] Mention may in particular be made, among alkyl radicals, of themethyl, ethyl, propyl, butyl, pentyl, isopropyl, tert-butyl, pentyl,hexyl, octyl, decyl or dodecyl radical.

[0069] The alkyne groups are radicals generally of 2 to 10 carbon atoms;they exhibit at least one acetylenic unsaturation, such as theacetylenyl radical.

[0070] The acyl group is a radical generally exhibiting from 1 to 20carbon atoms with a carbonyl group.

[0071] Mention may in particular be made, among aryl radicals, of thephenyl radical, optionally substituted in particular by a nitro orhydroxyl functional group.

[0072] Mention may in particular be made, among aralkyl radicals, of thebenzyl or phenethyl radical, optionally substituted in particular by anitro or hydroxyl functional group.

[0073] When R is a polymer chain, this polymer chain can result from aradical or ionic polymerization or from a polycondensation.

[0074] In the context of the present invention, preference is given tothe following control agents: xanthate compounds, dithiocarbamatecompounds and compounds of general formula (B).

[0075] Use is advantageously made, as control agent, of xanthatecompounds.

[0076] The process of the invention is carried out in the presence of asource of free radicals (initiator). However, for some monomers, such asstyrene, the free radicals which make it possible to initiate thepolymerization can be generated by the monomer possessing ethylenicunsaturation, itself at sufficiently high temperatures generally ofgreater than 100° C. It is not, in this case, necessary to add a sourceof additional free radicals.

[0077] The source of free radicals can be introduced into theminiemulsion or before the formation of the miniemulsion.

[0078] The source of free radicals which is of use in the process of thepresent invention is generally a radical polymerization initiator. Theradical polymerization initiator can be selected from the initiatorsconventionally used in radical polymerization. It can, for example, beone of the following initiators:

[0079] hydrogen peroxides, such as, in particular: tert-butylhydroperoxide, cumene hydroperoxide, t-butyl peroxyacetate, t-butylperoxybenzoate, t-butyl peroxyoctoate, t-butyl peroxyneodecanoate,t-butyl peroxyisobutyrate, lauroyl peroxide, t-amyl peroxypivalate,t-butyl peroxypivalate, dicumyl peroxide, benzoyl peroxide, potassiumpersulfate or ammonium persulfate,

[0080] azo compounds, such as, in particular:2,2′-azobis(isobutyronitrile), 2,2′-azobis(2-butanenitrile),4,4′-azobis(4-pentanoic acid), 1,1′-azobis(cyclohexanecarbonitrile),2-(t-butylazo)-2-cyanopropane,2,2′-azobis[2-methyl-N-(1,1)-bis(hydroxymethyl)-2-hydroxyethyl]propionamide,2,2′-azobis(2-methyl-N-hydroxyethyl]propionamide,2,2′-azobis(N,N′-dimethyleneisobutyramidine dichloride),2,2′-azobis(2-amidinopropane dichloride),2,2′-azobis(N,N′-dimethyleneisobutyramide),2,2′-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide),2,2′-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide),2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] or2,2′-azobis(isobutyramide) dihydrate,

[0081] redox systems comprising combinations, such as, in particular:

[0082] mixtures of hydrogen peroxide, alkyl peroxide, peresters,percarbonates and the like and of any iron salts or titanous salts, zincformaldehydesulfoxylate or sodium formaldehydesulfoxylate, and reducingsugars,

[0083] alkali metal or ammonium persulfates, perborates or perchloratesin combination with an alkali metal bisulfite, such as sodiummetabisulfite, and reducing sugars,

[0084] alkali metal persulfates in combination with an arylphosphinicacid, such as benzenephosphonic acid, and other similar compounds, andreducing sugars.

[0085] According to one embodiment, the amount of initiator to be usedis determined so that the amount of radicals generated is at most 50 mol%, preferably at most 20 mol %, with respect to the amount of thecontrol agent. In this case, the control agent corresponds to afunctional definition. Thus, it corresponds to the control agentspresent but also to the compounds present which exhibit the active partof a control agent (for example, the active part of RSC═SOR′ correspondsto —SC═SOR′).

[0086] The ethylenically unsaturated monomers of use in the process ofthe present invention are advantageously substantially water-insolublemonomers and generally exhibit a following general formula (I):

[0087] CXX′(═CV—CV′)_(b)═CH₂, in which:

[0088] V and V′, which are identical or different, represent: H, analkyl group or a halogen,

[0089] X and X′, which are identical or different, represent H, ahalogen or an R, OR, O₂COR, NHCOH, OH, NH₂, NHR, N(R)₂, (R)₂N⁺O⁻, NHCOR,CO₂H, CO₂R, CN, CONH₂, CONHR or CON(R)₂ group, in which R is selectedfrom alkyl, aryl, aralkyl, alkylaryl, alkene or organosilyl groups whichare optionally perfluorated and optionally substituted by one or morecarboxyl, epoxy, hydroxyl, alkoxy, amino, halogen or sulfo groups, and

[0090] b is 0 or 1.

[0091] The substantially water-insoluble monomers are preferablymonomers which exhibit a solubility in water of 0 to 5% by weight,advantageously of 1 to 3% by weight.

[0092] The ethylenically unsaturated monomers can be chosen inparticular from:

[0093] vinylaromatic monomers, such as styrene and styrene derivatives,such as α-methylstyrene or vinyltoluene,

[0094] ethylenic monomers, such as ethylene, α-olefins or vinylchloride,

[0095] dienes, such as butadiene, isoprene or chloroprene,

[0096] alkyl acrylates and methacrylates, the alkyl group of whichcomprises from 1 to 10 carbon atoms, such as methyl, ethyl, n-butyl,2-ethylhexyl, t-butyl, isobornyl, phenyl or benzyl acrylates andmethacrylates, and fluorinated monomers,

[0097] vinyl monomers, such as vinyl acetate, vinyl versatate or vinylpropionate, and nitriles, more particularly those comprising from 3 to12 carbon atoms, such as acrylonitrile and methacrylonitrile.

[0098] Use is preferably made of the following monomers:

[0099] styrene and styrene derivatives, such as α-methylstyrene orvinyltoluene,

[0100] vinyl nitriles,

[0101] dienes, for example butadiene or isoprene.

[0102] The term “(meth)acrylic esters” denotes esters of acrylic acid orof methacrylic acid with hydrogenated or fluorinated C₁-C₁₂ alcohols,preferably with C₁-C₈ alcohols. Mention may be made, among the compoundsof this type, of: methyl acrylate, ethyl acrylate, propyl acrylate,n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, t-butylacrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylateor isobutyl methacrylate.

[0103] The vinyl nitriles include more particularly those having from 3to 12 carbon atoms, such as, in particular, acrylonitrile andmethacrylonitrile.

[0104] For the preparation of poly(vinyl alcohol) blocks, use ispreferably made, as ethylenically unsaturated monomers, of carboxylicacid vinyl esters, such as, for example, vinyl acetate. The polymerobtained is then hydrolyzed at an acidic or basic pH.

[0105] The types and amounts of polymerizable monomers employedaccording to the present invention vary according to the specific finalapplication for which the polymer is intended. These variations are wellknown and can be easily determined by a person skilled in the art.

[0106] These ethylenically unsaturated monomers can be used alone or asa mixture.

[0107] According to a specific embodiment, in the process for thepreparation of a first generation polymer, if the ethylenicallyunsaturated monomer corresponds to the formula (I):CXX′(═CV—CV′)_(b)═CH₂, the first generation polymer obtained comprises ntimes the unit of formula (II):

[0108] with

[0109] n is greater than or equal to 1, preferably greater than 6,

[0110] V, V′, X, X′ and b being as defined above.

[0111] The surfactants which can be used in the context of the presentinvention comprise the anionic, cationic, amphoteric and nonionicemulsifiers commonly used in emulsion polymerization processes. They canbe used alone or as a mixture. A list of the surfactants which can beused in the context of the present invention can be found in“McCutcheon's Emulsifiers and Detergents 1981 Annuals”.

[0112] Use is preferably made of anionic surfactants. Mention may inparticular be made, among the latter, of alkylarylsulfonates, such assodium dodecylbenzenesulfonate, alkali metal alkyl sulfates, such assodium dodecyl sulfate (SDS), sulfonated alkyl esters, fatty acid estersor fatty acid salts, such as sodium stearate.

[0113] The surfactants can be employed in variable amounts which make itpossible to obtain a miniemulsification. To give an order of magnitude,the surfactants can be present in an amount of between approximately0.02 and 8.0% by weight, preferably between 0.3 and 5% by weight, withrespect to the total weight of ethylenically unsaturated monomerspresent.

[0114] The cosurfactants make it possible to increase the stability ofthe miniemulsion by minimizing the effects of Ostwald ripening.

[0115] These cosurfactants are generally substantially water-insolublecompounds, such as long-chain C₁₀-C₄₀ hydrocarbonaceous compoundsselected from alcohols, alkanes, mercaptans, carboxylic acids, ketones,amines and their mixtures. Mention may thus be made of hexadecane orcetyl alcohol. Use may also be made of polymeric cosurfactants and morespecifically of polymers (homopolymers or random, block or graftedcopolymers) which are substantially insoluble in water but soluble inthe monomer or the mixture of monomers used in the process according tothe invention. Mention may thus be made of polymers based on poly(methylmethacrylate), polystyrene, poly(vinyl acetate), poly(methyl acrylate)and poly(ethyl acrylate). Mention may in particular be made, as exampleof block copolymers, of polystyrene-polybutadiene-polystyrene andpolystyrene-polyisoprene. Mention may also be made of polymerspossessing active ends (active part of a control agent) obtainedaccording to a “living” or “controlled” radical polymerization method,such as described in particular in patent applications WO 98/58974, WO98/01478, WO 99/35178, WO 99/35177, WO 99/31144 and FR 2 802 208.Mention may also be made of silicone polymers possessing xanthate activeends, such as described in French patent application No. 009722, filedby the Applicant Company.

[0116] The number-average molecular mass (Mn) of the cosurfactant, whenthe latter is a polymer, is preferably between 10 000 and 1 000 000,preferably between 50 000 and 250 000 g/mol.

[0117] The amount by weight of cosurfactants with respect to theethylenically unsaturated monomer according to the process isadvantageously between 0.01 and 5%, preferably between 0.1 and 2%. Themolar ratio of cosurfactants to surfactant is advantageously between0.001 and 10, preferably between 0.5 and 5.

[0118] More particularly, the amount of surfactants and optionally ofcosurfactants is between 0.4 and 2% by weight with respect to the totalweight of ethylenically unsaturated monomers present.

[0119] The aqueous solution of the process according to the inventionthus comprises generally demineralized water. According to this process,the amount of water introduced can advantageously be relatively low. Itcan thus be such that the amount of dry matter at the end of the processaccording to the invention is between 10 and 65% by weight, preferablybetween 30 and 55%, with respect to the total weight of theminiemulsion.

[0120] A miniemulsion is thus a finely divided oil-in-water emulsion.More specifically, the mean diameter of the droplets corresponding tothe dispersed phase is between 10 and 500 nm. It can be preparedaccording to numerous methods. It is preferably obtained by subjectingto ultrasound or by shearing the emulsion comprising the compoundsspecified according to the present invention.

[0121] The process is preferably carried out semicontinuously.

[0122] In general, during the polymerization, the instantaneous contentof polymer with respect to the instantaneous amount of monomer andpolymer is between 50 and 99% by weight, preferably between 75 and 99%,or preferably still between 90 and 99%. This content is maintained, in aknown way, by controlling the temperature and the rate of addition ofthe reactants and optionally of the polymerization initiator.

[0123] The process is generally carried out in the absence of a UVsource by thermal initiation.

[0124] Thus, the temperature of the reaction (ii) can vary between 40°C. and 200° C. depending on the nature of the monomers used. It ispreferably between 60 and 120° C.

[0125] The pressure is generally in practice atmospheric pressure butcan be higher.

[0126] Advantageously, once the reaction (ii) is definitely complete,(iii) the miniemulsion is cooled to ambient temperature, (iv) thepolymer obtained is optionally isolated and (v) is optionally washedand/or dried.

[0127] The end of the reaction (ii) can be determined by determining thelevel of solid or by gas chromatography.

[0128] The process of the invention can be carried out starting from amixture of ethylenically unsaturated monomers. In this case, a randomfirst generation polymer is obtained. By selecting monomers of specificnatures and the amount of each of these monomers in the block, a blockhaving specific properties is obtained. This procedure is particularlyadvantageous when the first generation polymer thus obtained is anintermediate in the preparation of a block copolymer.

[0129] The present invention also relates to a process for thepreparation of an Nth generation block copolymer by radicalpolymerization, N being greater than or equal to 2, which comprises:

[0130] a first stage of radical polymerization as described above, toform the first generation polymer, followed by

[0131] N-1 stages of radical polymerization, each of these stages beingcarried out from a miniemulsion, as described above, comprising:

[0132] at least one ethylenically unsaturated monomer,

[0133] the polymer obtained in the preceding radical polymerizationstage,

[0134] optionally an aqueous solution,

[0135] optionally a surfactant, preferably in a low amount,

[0136] and (ii) the reaction of said emulsion, in the presence of asource of free radicals, at a sufficient temperature and/or for asufficient time to form polymers, the ethylenically unsaturated monomeror monomers being such that the block formed at this stage is differentin nature from the block formed in the preceding stage.

[0137] According to one embodiment of the invention, (1) a firstgeneration polymer is synthesized from a miniemulsion and subsequently(2) the first generation polymer obtained in stage (1) is used toprepare a (second generation) diblock copolymer by bringing this firstgeneration polymer into contact, in a miniemulsion, with one or moreethylenically unsaturated monomers and a source of free radicals, the,block obtained in stage (2) being different in nature from the firstgeneration polymer from stage (1).

[0138] This stage (2) can be repeated with new monomers and the diblockcopolymer obtained to synthesize a new block and to obtain a triblockcopolymer.

[0139] The polymerization stage can thus be repeated as many times asnecessary from a block copolymer in order to obtain a copolymer with anadditional block.

[0140] The process of the invention thus makes it possible to obtain adiblock copolymer comprising two blocks of formula (III):

[0141] from a miniemulsion comprising:

[0142] an ethylenically unsaturated monomer of formula (IIB);CYY′(CW═CW′)_(a)═CH₂,

[0143] a first generation polymer as described above,

[0144] n and n′, which are identical or different, are greater than orequal to 1,

[0145] V, V′, W and W′, which are identical or different, represent: H,an alkyl group or a halogen,

[0146] X, X′, Y and Y′, which are identical or different, represent H, ahalogen or an R, OR, O₂COR, NHCOH, OH, NH₂, NHR, N(R)₂, (R)₂N⁺O⁻, NHCOR,CO₂H, CO₂R, CN, CONH₂, CONHR or CON(R)₂ group, in which R is selectedfrom alkyl, aryl, aralkyl, alkylaryl, alkene or organosilyl groups whichare optionally perfluorated and optionally substituted by one or morecarboxyl, epoxy, hydroxyl, alkoxy, amino, halogen or sulfo groups, and

[0147] a and b, which are identical or different, have the value 0 or 1.

[0148] The ethylenically unsaturated monomers which are of use are thosedescribed above.

[0149] According to this process for the preparation of block polymers,when it is desired to obtain block polymers which are homogeneous andnot possessing a composition gradient, and if all the successivepolymerizations are carried out in the same reactor, it is essential forall the monomers used during one stage to have been consumed before thepolymerization of the following stage begins, thus before the newmonomers are introduced.

[0150] When it is desired to obtain a random block, the polymerizationstage is carried out with a composition comprising a mixture ofethylenically unsaturated monomers.

[0151] The present invention also relates to the first generationpolymers and to the block polymers capable of being obtained accordingto any one of the processes of the invention. These polymers exhibit acontrolled molecular mass.

[0152] According to a specific embodiment, the block polymers compriseat least three polymer blocks selected from the following combinations:

[0153] polystyrene/polymethylstyrene/polystyrene,

[0154] polystyrene/poly(ethyl acrylate)/polystyrene,

[0155] polystyrene/poly(butyl acrylate)/polystyrene,

[0156] polystyrene/poly(tert-butyl acrylate)/polystyrene,

[0157] polystyrene/polyvinylpyridine/polystyrene,

[0158] polystyrene/polybutadiene/polystyrene,

[0159] polystyrene/polyisoprene/polystyrene

[0160] in 7 g of water are added, at the same time as the addition of 53g of styrene for 30 minutes is begun. The reaction is halted 2 h 30 minafter the end of the introduction of the styrene.

[0161] Results: TABLE 1 Sample conv. %^(a)) Mn _(GPC) ^(b)) Mn _(theor)^(c)) Mw/Mn^(d)) D_(p) (nm)^(e)) First block: 99 134 000  98 500 6.9 94Poly(butyl) acrylate Block 100 117 200 115 000 5.7 97 copolymer:Polystyrene/ Poly(butyl acrylate)/ Polystyrene

[0162] It is found that the value of Mn for the final copolymer is closeto the theoretical value. Nevertheless, the value of the polydispersityindex is high (equal to 6.7).

EXAMPLE 2

[0163] Preparation of a miniemulsion polystyrene-poly(butylacrylate)/polystyrene block copolymer in the presence of diethylmeso-2,5-di(O-ethyl xanthate)adipate EtO(C═S)S—C(CO₂Et)C₂H₄(CO₂Et)C—S(C═S)OEt

[0164] A solution of sodium dodecyl sulfate (1.56 9; 0.5% by weight withrespect to the butyl acrylate), of sodium hydrogencarbonate (0.2 g) andof initiator 4,4′-azo(4-cyanopentanoic acid) (0.45 g; 50 mol % withrespect to the xanthate) in water (540.0 g) is mixed with a solution ofdiethyl meso-2,5-di(O-ethyl xanthate)adipate (1.43 g; 0.00323 mol) andhexadecane (4.88 g) in n-butyl acrylate (315.0 g). The mixture issubsequently homogenized for 5 minutes by mixing at 24 000 rpm and bysubjecting to ultrasound for 5 minutes using a device of the Branson1200 type.

[0165] The pre-miniemulsion prepared according to the method describedabove is introduced into a 5-necked reactor equipped with a refluxcondenser, a thermocouple and a mechanical stirrer. The temperature isset at 70° C. The reaction mixture is stirred at a speed of 250 rpm atfor 4 hours. A 40 g sample is subsequently withdrawn from the reactionmedium (first block: Poly(n-butyl acrylate)). After this sample has beenwithdrawn, 0.23 g of 4,4′-azo(4-cyanopentanoic acid) in 10 g of water isintroduced at the same time as 0.03 g of sodium hydroxide. 53 g ofstyrene are then added continuously over 30 minutes. 5 hours after theend of the introduction of the styrene, the reaction is halted bycooling to ambient temperature.

[0166] Results: TABLE 2 Sample % conv. Mn_(GPC) Mn_(theor) Mw/Mn D_(p)(nm) First block: 97 92 400  97 700 1.95 287 Poly(butyl acrylate) Block96 90 200 114 900 2.96 295 copolymer: Polystyrene/ Poly(butyl acrylate)/Polystyrene

[0167] From the results given in table 2, it is apparent that theminiemulsion system makes it possible to considerably reduce thepolydispersity index. The distribution in the molecular masses which isobtained is monomodal. Furthermore, the use of GPC double detection(refractometer (RI) and UV at 254 nm) makes it possible to be positivethat a triblock copolymer is indeed formed (superposition of the two RIand UV plots).

[0168] In addition, the distribution in particle sizes is very narrow:less than 0.01 for the first miniemulsion poly(butyl acrylate) block,0.03 for the triblock.

EXAMPLE 3

[0169] Preparation of a miniemulsion polystyrene-poly(butylacrylate)/polystyrene block copolymer in the presence of diethylmeso-2,5-di(O-ethyl xanthate)adipate EtO(C═S)S—C(CO₂Et)C₂H₄(CO₂Et)C—S(C═S)OEt

[0170] A solution of sodium dodecyl sulfate (1.56 g; 0.37% by weightwith respect to the monomers), of sodium hydrogencarbonate (0.2 g) andof potassium persulfate (0.39 g; 50 mol % with respect to the controlagent) in water (540.0 g) is mixed with a solution of diethylmeso-2,5-di(O-ethyl xanthate)adipate (1.43 g; 0.00323 mol) and ofhexadecane (4.88g) in n-butyl acrylate (315.0 g). The medium issubsequently homogenized for 5 minutes by stirring at 9 500 rpm and thenby subjecting to ultrasound for 5 minutes using a device of the Branson1200 type.

[0171] The pre-miniemulsion prepared as described above is charged to astainless steel reactor. The reaction mixture is subsequently degassedat ambient temperature by a stream of nitrogen with stirring (250 rpm)and then the temperature is brought to 70° C. The mixture is maintainedat this temperature for 6 hours. A 40 g sample is then withdrawn (firstblock: Poly(n-butyl acrylate)), this operation being followed byaddition of a solution of initiator (0.20 g) in water (40.0 g). At thispoint, 110 of styrene are added over 10 minutes. After this addition,the reaction is prolonged for 5 hours and is then cooled to ambienttemperature.

[0172] Results TABLE 3 P. size Sample % conv. Mn_(GPC) Mn_(theor) Mw/Mn(nm) First block: 99  94 500  98 200 2.19 184 Poly(butyl acrylate) Block99 128 000 131 500 3.03 193 copolymer: Polystyrene/ Poly(butylacrylate)/ Polystyrene

[0173] These results show that Mn is fully controlled. RI and UV at 254nm double detection by GPC confirms the expected triblock structure. Inaddition, the distribution in particle sizes is narrow (<0.1).

EXAMPLE 4

[0174] Preparation of a miniemulsion polystyrene-poly(butylacrylate)/polystyrene block copolymer in the presence of diethylmeso-2,5-di(O-ethyl xanthate)adipateEtO(C═S)S—C(CO₂Et)C₂H₄(CO₂Et)C—S(C═S)OEt

[0175] A solution of sodium dodecyl sulfate (1.56 g; 0.42% by weightwith respect to the monomers), of sodium carbonate (0.3 g) and ofpotassium persulfate (0.84 g; 50 mol % with respect to the controlagent) in water (540.0 g) is mixed with a solution of diethylmeso-2,5-di(O-ethyl xanthate)adipate (3.1 g; 0.007 mol) and ofpolystyrene (2.25 g, Mn=50 000 g/mol, Mw/Mn=5) in n-butyl acrylate(245.0 g). The medium is subsequently homogenized for 5 minutes bystirring at 24 000 rpm and then by subjecting to ultrasound for 5minutes using a device of the Branson 1200 type.

[0176] The pre-miniemulsion prepared as described above is charged to astainless steel reactor. The reaction mixture is subsequently degassedat ambient temperature by a stream of nitrogen with stirring (250 rpm)and then the temperature is brought to 70° C. The mixture is maintainedat this temperature for 6 hours. A 5 g sample is then withdrawn (firstblock: Poly(n-butyl acrylate)), this operation being followed by theaddition of a solution of initiator (0.42 g) in water (40.0 g). At thispoint, 115 g of styrene are added over 10 minutes. After this addition,the temperature is brought to 80° C. and the reaction is prolonged for 5hours and is then cooled to ambient temperature. TABLE 4 Sample % conv.Mn_(GPC) Mn_(theor) Mw/Mn First block: 99 41 500 35 400 1.56 Poly(butylacrylate) Block copolymer: 99 53 500 50 400 2.25 Polystyrene/ Poly(butylacrylate)/ Polystyrene

[0177] These results show that Mn is fully controlled. RI and UV at 254nm double detection by GPC confirms the expected triblock structure. Inaddition, the distribution in particle sizes is very narrow (<0.05).

1. A process for the preparation of first generation polymers by radicalpolymerization which comprises (i) the preparation of a miniemulsioncomprising: at least one ethylenically unsaturated monomer, at least onecontrol agent selected from xanthates, dithiocarbamates,thioether-thiones, xanthates comprising phosphorus and optionallyfluorine and dithiophosphoric acid esters, an aqueous solution, at leastone surfactant, and a cosurfactant, and (ii) the reaction of saidminiemulsion, in the presence of a source of free radicals, at asufficient temperature and/or for a sufficient time to form polymers. 2.The process as claimed in the preceding claim 1, characterized in thatwherein the control agent is selected from xanthates, dithiocarbamates,thioether-thiones, and xanthates comprising phosphorus and optionallyfluorine and dithiophosphoric acid esters.
 3. The process as claimed inclaim 1 or 2, characterized in characterized in that wherein the controlagent is a compound of xanthate type.
 4. The process as claimed in anyone of the preceding claims claim 1, characterized in that wherein thesource of free radicals is a radical polymerization initiator selectedfrom hydrogen peroxides, azo compounds and a redox system.
 5. Theprocess as claimed in any one of the preceding claims claim 1, in whichthe ethylenically unsaturated monomer is a substantially water-insolublemonomer and corresponds to the following formula (I):CXX′(═CV—CV′)_(b)═CH₂ and the first generation block polymer obtainedcomprises n times the unit of formula (II):

 with n is greater than or equal to 1, preferably greater than 6, V andV′, which are identical or different, represent a hydrogen atom, analkyl group or a halogen, X and X′, which are identical or different,represent H, a halogen or an R, OR, O₂COR, NHCOH, OH, NH₂, NHR, N(R)₂,(R)₂N⁺O⁻, NHCOR, CO₂H, CO₂R, CN, CONH₂, CONHR or CON(R)₂ group, in whichR is selected from alkyl, aryl, aralkyl, alkylaryl, alkene ororganosilyl groups which are optionally perfluorated and optionallysubstituted by one or more carboxyl, epoxy, hydroxyl, alkoxy, amino,halogen or sulfo groups, and b is 0 or
 1. 6. The process as claimed inone of the preceding claims claim 1, characterized in that wherein thesurfactant is an anionic surfactant.
 7. The process as claimed in thepreceding claim 6, characterized in that wherein the anionic surfactantis selected from alkylarylsulfonates, alkali metal alkyl sulfates,sulfonated alkyl esters, fatty acid esters and fatty acid salts.
 8. Theprocess as claimed in one of the preceding claims claim 1, characterizedin that wherein the cosurfactant is a long chain C₁₀-C₄₀hydrocarbonaceous compound selected from alcohols, alkanes, mercaptans,carboxylic acids, ketones, amines, polymers and their mixtures.
 9. Theprocess as claimed in any one of the preceding claims claim 1,characterized in that wherein the amount of surfactants is betweenapproximately 0.02 and 8.0% by weight, preferably between 0.3 and 5% byweight, with respect to the total weight of ethylenically unsaturatedmonomers.
 10. The process as claimed in any one of the preceding claimsclaim 1, characterized in that wherein the amount by weight ofcosurfactants with respect to the ethylenically unsaturated monomeraccording to the process is advantageously between 0.01 and 5%,preferably between 0.1 and 2%,04.
 11. The process as claimed in any oneof the preceding claims claim 1, characterized in that wherein the molarratio of cosurfactants to surfactant is between 0.001 and 10, preferablybetween 0.5 and
 5. 12. The process as claimed in any one of thepreceding claims claim 1, characterized in that wherein the amount ofsurfactants and optionally of cosurfactants is between 0.4 and 2% byweight with respect to the total weight of ethylenically unsaturatedmonomers.
 13. The process as claimed in any one of the preceding claimsclaim 1, characterized in that wherein the amount of dry matter at theend of the process is between 10 and 65% by weight, preferably between30 and 55% , with respect to the total weight of the miniemulsion. 14.The process as claimed in any one of the preceding claims claim 1,characterized in that wherein the temperature of the reaction (ii)varies between 40° C. and 200° C.
 15. A process for the preparation ofan Nth generation block copolymer by radical polymerization, N beinggreater than or equal to 2, which comprises: a first stage of radicalpolymerization as described above, to form the first generation polymer,followed by N-1 stages of radical polymerization, each of these stagesbeing carried out from a miniemulsion, described according to one of thepreceding claims claim 1, comprising: at least one ethylenicallyunsaturated monomer, the polymer obtained in the preceding radicalpolymerization stage, optionally an aqueous solution, optionally asurfactant, and (ii) the reaction of said emulsion, in the presence of asource of free radicals, at a sufficient temperature and/or for asufficient time to form polymers, the ethylenically unsaturated monomeror monomers being such that the block formed at this stage is differentin nature from the block formed in the preceding stage.
 16. The processas claimed in the preceding claim 15 for the preparation of a secondgeneration block copolymer, which comprises the radical polymerizationof a composition comprising: at least one ethylenically unsaturatedmonomer, a source of free radicals, and the first generation polymerobtained according to the prcess of one of claims 1 to
 14. 17. Theprocess as claimed in claim 16 for the preparation of a diblockcopolymer comprising two blocks of formula (III):

from the miniemulsion comprising: an ethylenically unsaturated monomerof formula (IIB); CYY′(CW═CW′)_(a)═CH₂, a first generation polymerobtained by the process as claimed in one of claims 1 to 14, n and m,which are identical or different, are greater than or equal to 1, V, V′,W and W′, which are identical or different, represent: H, an alkyl groupor a halogen, X, X′, Y and Y′, which are identical or different,represent H, a halogen or an R, OR, O₂COR, NHCOH, OH, NH₂, NHR, N(R)₂,(R)₂N^(+O) ⁻, NHCOR, CO₂H, CO₂R, CN, CONH₂, CONHR or CON(R)₂ group, inwhich R is selected from alkyl, aryl, aralkyl, alkylaryl, alkene ororganosilyl groups which are optionally perfluorated and optionallysubstituted by one or more carboxyl, epoxy, hydroxyl, alkoxy, amino,halogen or sulfo groups, and a and b, which are identical or different,have the value 0 or
 1. 18. The process as claimed in any one of thepreceding claims claim 1, in which the ethylenically unsaturated monomeris selected from styrene and styrene derivatives, such asα-methylstyrene or vinyltoluene, vinyl halides, vinyl nitriles ordienes, for example butadiene or chloroprene.
 19. A polymer capable ofbeing obtained prepared by a process as defined according to one of thepreceding claims claim
 1. 20. The polymer as claimed in either of claims18 and 19 claim 18, characterized in that it which exhibits at leastthree polymer blocks.
 21. The polymer as claimed in the preceding claim20, in which wherein the three blocks are selected from the followingcombinations: polystyrene/polymethylstyrene/polystyrene,polystyrene/poly(ethyl acrylate)/polystyrene, polystyrene/poly(butylacrylate)/polystyrene, polystyrene/poly(tert-butylacrylate)/polystyrene, polystyrene/polyvinylpyridine/polystyrene,polystyrene/polybutadiene/polystyrene,polystyrene/polyisoprene/polystyrene, poly(vinyl acetate)/poly(butylacrylate)/poly(vinyl acetate).